Dash 80

The story of the prototype 707.

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It was not the size but the design of the wings and engine mounts that gave Boeing its most important lead over its competitor.  The 35-degree sweep of the wing and tail had been established through research that included a series of flights in a Bell L-39, which was a Bell P-63 with its wings swept.  The same angle had been used on both the B-47 and B-52.  With this angle, Dash 80 turned out to be 20 mph faster than the DC-8, with its 30-degree sweep.

The practice of mounting engines in pods on pylons below the wing began in 1947 with the B-47.  Suspending the engines from pylons left room in the wings for fuel tanks.  And in a crash landing, a pod could break away without damaging a wing or rupturing one of its fuel tanks.  Unlike the bombers, which had their engines in pairs, Dash 80’s design called for a single engine in each pod, so if an engine blew up, it wouldn’t damage its neighbor.  The arrangement also provided a more even distribution of the engine’s weight and allowed for lighter wings.  And the pods opened up so that airline mechanics had easy access to each engine.

It was an impressive design, but not perfect: Dash 80 had some bugs in its tail assembly and landing gear, and test pilots Johnston and Richard “Dix” Loesch, along with engineer James Gannett, were responsible for shaking them out.  Boeing could not have brought together three more diverse personalities.  Chief pilot Johnston had all the swagger you expect in someone named Tex, though he could be reserved when he talked about airplanes.  Gannett was his exact opposite, wiry and quiet.  Loesch was the most reflective of the trio and easily the most emotional about the project and his memories of those days.  But then, it was his luck to catch some of Dash 80’s wildest rides.

Landing an 80-ton airplane at speeds of 150-mph and less had been done before.  But using only the wheel brakes to get one stopped within 6,000 feet on a wet or icy runway hadn’t, and that was as much room as the largest airports of the day had to offer.  Large military aircraft landed on 10,000-foot runways with the assistance of a drag chute, an impractical system for airline operations.

Faced with these constraints, Boeing designers gave Dash 80 thrust reversers to accomplish what the reversing propellers on piston-engine aircraft did to reduce ground roll distances after landing.  After evaluating three final candidates, the designers chose the folding W-shaped design that is now seen on the aft end of almost all jet engines.  They also came up with a new version of the conventional tricycle landing gear, one that gave test pilots and engineers many headaches.

On the eve of the scheduled maiden flight, the left main gear collapsed after some taxiing tests.  “Well, now is the time to learn these things,” Johnston said as he stepped out of the airplane.  Dash 80 lay on the ground like an exhausted bird.  At least the gear had performed as advertised: it broke away without damaging the wing or the fuel tanks.  Dash 80’s first flight was postponed while engineers beefed up the gear structure and healed minor wounds.

Less than a month later, the airplane lost its nose gear.  It happened after Johnston had been heating up the brakes with a series of high-speed ground runs and stops, then taking off to see what happened in the cold temperatures aloft—“cold soaking,” as engineers called it.  What happened was an expansion of the hydraulic fluid on the ground and a contraction in the air.  Unbeknown to Johnston, the hydraulic system responded by forming bubbles in the lines, which sensors interpreted as a broke brake line.  Performing as designed, the sensors promptly shut off fluid flow to the brakes.

Johnston landed daintily, stepped on the brakes, and realized he had none.  On one side of the field sat a row of private aircraft; on the other, a line of B-52s.  Johnston had one place to go: a grassy median between the two runways.  He hoped the soft earth would slow Dash 80 enough to let him swing the airplane around and roll to a stop.  He recalls a sudden crunch.  Contractors making runway repairs had left a big block of concrete exactly where Dash 80 would find it.  It knocked the nose gear off and damaged the belly, but Boeing had Dash 80 flying again in about three days.  A redesign of the braking system sensors solved the hydraulics problem.

Not long after that, Dash 80 chalked up a midair landing gear explosion and fire when the new anti-skid brakes turned out to be spectacularly efficient heat reservoirs.  Johnston had heated the brakes doing ground runs, then had flown with the wheels down for 15 minutes to cool them.  But as soon as the landing gear was retracted, there were several explosions accompanied by the smell of burning rubber.  “There was smoke everywhere,” he recalls, “so I speeded up, put the gear down, and blew the fire out.”  He didn’t need brakes to stop after landing—5 of the 10 tires were flat.

The final thrill involving Dash 80’s gear occurred during a test of the thrust reversers.  After a series of landings, a hydraulic line let go and the flammable fluid leaked out onto a hot brake.  The resulting blaze caused the crew to holler for the fire truck and abandon ship.  Boeing replaced the entire hydraulic system with one that used less flammable liquid.  “It was just another part of the learning curve,” Gannett said.

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